The present invention relates to flat cables and, more particularly, to repair and reinforcement of already fabricated flexible flat cables.
Flexible flat cables are subject to tearing which will propagate from their edges and to and through the conductors. Such tearing can occur during handling, assembly and use of the cable, and originates at micro-fissures, micro-cuts, notches or other imperfections existing along the edges of the cable. These imperfections are formed during fabrication of the cable after the copper foil and fabric reinforcements have been laminated into the flat cable preform, when the cable is cut to its final shape by steel rule dies.
Tearing has been a long-known problem, and many solutions have been advanced. One such solution appears in U.S. Pat. No. 4,812,135. There, a thread of Kevlar (trademark of E.I. Du Pont DeNemours & Co.) material is incorporated internally within the flat cable and parallel to the edge of the conductors, at the edges of the flexible circuit strip. By including reinforcing thread members between two layers of the flexible cable, any tears are prevented from growing further into the cable past the reinforcing thread members. That disclosure also describes an alternative embodiment in which the reinforcing thread is placed internally of the layers during manufacture, and is bonded to the outer surface of one layer of a cable.
Such a design has some disadvantages. It is not amenable to ready made and/or designed cables, which require high pressure when laminated. Placing the reinforcing thread within such an already fabricated cable is virtually impossible. This design is also not amenable to selective use, that is, it may not be necessary to utilize a reinforcing thread for all designs, but only for selected designs where reinforcement is needed. Most importantly, while that solution recognizes the problems of tears, it does not cure the defect or imperfection; it merely uses a reinforcing thread to prevent further propagation of the tear through the cable.